I have an 02 X-type Sport, 3.0L with 126,000 miles on her. Ran fine in the warm weather but very rough when first starting up in the cold (I'm from FL so that means less than 50 deg. Farenheit). I got some misfire codes so I figured with the mileage it was probably the plugs so I changed those out along with the 3 rear coils - and now it runs slightly smoother when starting in the cold, but shudders when accelerating with any intensity - at about 40 MPH, very slow acceleration doesn't cause any problems and there's nothing noticeable before 40 mph. This didn't happen before I changed the plugs. No codes are coming up.
I have already changed the PCV hose connection to the newer waffle design and the Brake Booster Vacuum Hose / Valve.
One thing I did notice while reconnecting everything was that the hose that runs from the rear passenger side top of the engine to the ribbed air intake just on the intake side of the air filter box was very brittle and broke off a bit, think I got it back together ok but maybe should just replace - does anyone know the name of that hose (actually 2 hoses with a 90deg elbow connection.
Oh, and the yellow intake manifold gaskets looked fine (at least the two I could see from sliding the manifold over (didn't disconnect from Air intake during the plug change as I couldn't disconnect the hose clamps) so I didn't replace those.

Any help is appreciated. - thanks

 

Well, I'm getting no help - so thought I'd add my most recent findings, when I put the car into sport mode - it runs much better, also noticed a clicking noise at the throttle body when turning the car off, which may be normal but not sure.
thanks

 

I have a similar shuddering that starts at about 40 mph while accelerating, but goes away by about 60 mph. It does not happen if I accelerate slowly. My car is a 2002 X-type 2.5L automatic with 34000 miles. No codes are coming up. I feel the shuddering through the steering wheel. Could this be the transfer case? Or the transmission? Maybe a bent wheel, wheel alignment or wheel balance?

 

I am now sure that mine is the transmission slipping. While traveling between 40-50 mph, I suddenly gave it more throttle, and the RPM's shot up without causing much acceleration. So that appears to be a clutch slipping, probably the 4th gear clutch. I plan to take it to AAMCO this weekend.

 

i had a simalr problem when i got mine first. Mine was a bad fuel system...maybe check fuel delivery? Im just shooting int he dark. Are there any other nioses?

 

There are no unusual noises, no CEL, no codes. A bad fuel system cannot cause the engine to race without producing acceleration - that has to be something between the engine and the wheels. So it could possibly be the transfer case, but most likely the transmission.

 

Still happening, maybe the fuel delivery is the problem as it doesn't happen when accelerating very slowly, or when I really get on it, just the normal acceleration is what it doesn't seem to like up around the 35-40 mph ranges. If I drive her like a race car she's fine.
Is there a specific procedure for tightening the upper intake manifold back down? I wonder if it could be seated poorly and a tiny leak might only be noticeable under the aforementioned conditions?
thanks for the help.

 

Matt - If there are no codes, I don't think it is likely to be a fuel system problem. The computer seems to be pretty good at catching that kind of problem. I would be looking for possible transmission problems. Have you changed the transmission fluid, or checked the level? But I would replace that brittle hose anyway.